Recreation impact on the early establishment of dune-building grasses Elytrigia juncea and Ammophila arenaria on the beach

Summary

Sandy shores serve multiple ecosystem services, including recreation. To what extent these services can coexist is unclear, especially given increasing stressors such as rising sea levels and urbanization. We investigated the effect of recreational pressure on the establishment of two dune building grass species representative for European beaches (Ammophila arenaria and Elytrigia juncea). We conducted a field introduction experiment with seeds and rhizomes (diaspores) of both species along an anthropogenic pressure gradient on the upper beach of the Dutch barrier Island of Terschelling. Across two beach sites 300 plots were set out following a randomised block design with 4 factorial treatments (species*diaspore). Local plant material was collected. Plots were left unmarked to enable undisturbed recreation. Establishment success was monitored by counting the number of emerged shoots per plot at regular intervals across the growing season of 2022. To control for environmental drivers, we included the environmental variables: soil moisture, bed level change, and distance to the sea. We found that establishment success increased significantly with longshore distance from the beach entrance, irrespective of species or diaspore type. This effect was especially strong within the first 100 m, where plants did emerge from seeds or rhizomes but progressively died over the summer. Establishment success was further constrained by changes to the beach bed level and distance to the sea. Our results indicate that recreational pressure can constrain dune development on the upper beach. This implies trade-offs between beach functions, that should be considered when designing sandy coastal areas.